Conventional molding apparatuses used in die casting, injection molding and the like generally include a fixed plate that supports a fixed die, a movable plate that supports a movable die, and a support plate. A plurality of tie bars (normally, four) are inserted through and extend from the movable plate and have respective end portions that are fixed to the fixed plate and the support plate. A die clamping mechanism is disposed between the support plate and the movable plate. Accordingly, a structure is provided in which closing and clamping of the die are performed by moving the movable plate along the tie bars toward the fixed plate side. With the type of molding apparatus, as the die clamping mechanism in large-sized molding apparatuses, a toggle type die clamping mechanism is often used since it enables a large clamping force to be generated in resistance to the substantial internal die pressure.
However, recently, it is becoming common for production lines to carry out small batch multiple product production, and thus the cycle of die replacement is becoming shorter. Further, as a result of tougher demands for product accuracy and productivity, there has been a tendency for injection pressure and injection speed to be raised more and more. This has been accompanied by an unavoidable shortening in die life, and as a result there has been an increase in the frequency of die replacement. However, conventionally, with general-use die casting machines or injection molding apparatus, a plurality of tie bars are disposed around the fixed die and the movable die as previously described. Accordingly, a problem has arisen in that the tie bars form an obstruction to the die replacement operation (change over). Moreover, with the toggle type die clamping mechanism, in addition to the fact that the components (links etc.) configuring the toggle mechanism are complicated and large sized, it is necessary to provide a die clamping cylinder with a long stroke. Thus, a problem occurs in that an increase in installation space is unavoidable.
To address this, recently, various types of molding apparatus have been investigated which do not require tie bars and which allow the toggle type clamping mechanism to be disused. For example, Japanese Patent Laid-Open Publication No. Hei. 8-72113 discloses a molding apparatus in which: a die opening-closing cylinder is disposed between a fixed die plate (fixed plate) and a movable die plate (movable plate) and moves the movable plate forward and backward with respect to the fixed plate to perform opening and closing of a movable die with respect to a fixed die; connecting-fixing means (tie bar fixing means) disposed at a rear surface side of the fixed plate and the movable plate for fixing a tie bar in a removable manner to both plates; and a die clamping cylinder which is disposed in the vicinity of a tie bar insertion hole of the fixed plate or the movable plate and which generates a die clamping force that pushes the movable plate toward the fixed plate side using the tie bar fixing means and the tie bar. Moreover, Japanese Patent Laid-Open Publication No. Hei. 8-117959 discloses a molding apparatus in which, in a structure that is the same as that described above, a dedicated tie bar removal cylinder is provided separately from a die opening-closing cylinder.
With these molding apparatus, if fixing of the tie bar with respect to the fixed plate side is released, and the die opening-closing cylinder or the tie bar removal cylinder is activated and extended, the tie bar is removed from the fixed plate. Thus, it is possible to remove the tie bar from the fixed plate and perform change over without the tie bar causing interference. In addition, die clamping is performed using the die clamping cylinder, and thus these molding apparatus have the advantage that the complicated toggle type die clamping mechanism can be disused.
However, according to the molding apparatus disclosed in Japanese Patent Laid-Open Publication No. Hei. 8-72113 and Japanese Patent Laid-Open Publication No. Hei. 8-117959, in either structure, the die opening-closing cylinder is disposed transversely between the fixed plate and the movable plate. Thus, a problem occurs in that the space that can be effectively used for change over is inadequate.